Record crowds were on hand to witness one of the fastest races in the world.

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INDIANAPOLIS—When it comes to American sporting traditions, there are few events as storied as the Indianapolis 500. It's a 500-mile test of speed, endurance, and bravery that takes place at the end of May. It takes place at the Indianapolis Motor Speedway, a 2.5-mile (4km) race track that's not only the oldest of its kind but also the largest sporting venue anywhere on Earth. And this year's Indy 500 is a special one—it's the race's 100th running. With speeds well in excess of 200mph (321km/h), it's the fastest race on the motorsports calendar, and this year Ars was in attendance along with more than 350,000 other race fans to take in what's often called the greatest spectacle in racing.

The Track

As we'll see, the cars have changed a lot over the course of those hundred runnings. And the race has gone through good times—with crowds topping 400,000—and bad. There's been innovation and more than its fair share of tragedy. But throughout it all the track has remained a constant. Well, almost.

The Indianapolis Motor Speedway was built in 1909 by Carl Fisher, who wanted to create a venue for the nascent American auto industry to test its new-fangled creations. Initially, all 2.5 miles of the track's surface were made of crushed stone, something that proved conducive to a series of fatal accidents that started with the inaugural car race held on August 19 of that year. As the death toll mounted over the next few days, Fisher and his partners made the wise decision to pave it. They opted for bricks—more than 3.2 million of them—leading locals to dub the speedway "the Brickyard."

Eventually, this surface also proved too dangerous for racing, and the track was progressively repaved with asphalt, a process that happened in stages in the late 1930s and then completely in 1961. Today, just a single yard (0.9m for those of you that speak metric) remains at the start-finish line.

It's a simple-enough looking circuit: two long straights, two short straights, and four left-hand, banked turns. But racing on it is anything but simple, particularly at more than 200mph for hours at a time. It's also enormous. It's hard to appreciate the scale of the place unless you've been there. Crowds of 150,000 make it look empty, and it dwarfs every other permanent sporting arena you can think of.

The first Indy 500 was held in 1911 over the last weekend in May, a couple of years after the paving was complete. 40 cars were entered, and the technical regulations merely specified that one's engine couldn't be bigger than 600 cubic inches (9.8 liters), and the car had to be capable of at least 75mph (120km/h). That race was won by Ray Harroun's Marmon Wasp, although not without controversy (Ralph Mulford claimed a scoring error meant his car had traveled more distance by the time Harroun crossed the finish line).

A tradition was born that day, and ever since—barring interruptions from World Wars—this temple of speed has held its highest and holiest celebration over the weekend that precedes what we now call Memorial Day. There's room on the grid for just 33 cars, and while it's true that in some years the race has struggled to attract that many (particularly after the disastrous "split" that occurred in 1996 when a breakaway series was formed), in other years the entry list has been massively oversubscribed. In 1984, for example, 117 cars fought it out in the early weeks of May to qualify for those coveted 33 spots.

The Technology

The starting line-up at the first ever Indianapolis 500 motor race at Indianapolis Motor Speedway in Speedway, Indiana, 1911. Front row, left to right: Johnny Aitken (1885 - 1918) in a National car, number 4, Harry Endicott (1883 - 1913) in an Inter-State, car number 3, Ralph DePalma (1882 - 1956) in a Simplex, car number 2 and Lewis Strang (1887 - 1911) in a J.I. Case, car number 1.

Getty Images | Archive Photos

Ray Harroun's Marmon Wasp now resides in the track's museum.

Jonathan Gitlin

The 1931 Cummins Diesel wasn't fast, but it did complete the whole 500 miles without needing to stop to refuel.

Jonathan Gitlin

1941's winner is notable for having not one but two drivers. Floyd Davis started the race but the car's owner replaced him on lap 72 with Mauri Rose.

Jonathan Gitlin

Jim Clark changed Indy for ever in 1965 when he won in the Lotus 38. Front engines were out and never won again.

This bright red wedge is the Lotus turbine car.

Jonathan Gitlin

You don't get paint schemes like this in racing any more. Al Unser first raced this Lola T150 at Indy in 1968, when it had all-wheel drive. That was banned the following year and the car competed again, this time just powering the rear wheels. Neither of those two races were successful for Unser, but he and the car returned in 1970 and this time won it.

Jonathan Gitlin

Smokey Yunick's pod car. I think the kids' expressions say it all.

Jonathan Gitlin

By the early 1970s, the tires were slick and the bodies covered in wings.

Jonathan Gitlin

Aerodynamics continued to be refined in the 1980s, as speeds rose higher and higher.

No team owner has been as successful as "The Captain," Roger Penske. These are some of his winning cars, starting with Mark Donohue's Offy-engined McLaren.

Yet more of the Captain's victory machines. The one in the middle is the infamous Penske PC-23, powered by that pushrod Mercedes 500I.

Jonathan Gitlin

Today's turbocharged, bewinged, mid-engined carbon-fiber creations would be unrecognizable to the contestants from the early days. This is unsurprising, given how much the automobile has evolved in 105 years. The early years featured all manner of machines, some crewed by a driver and mechanic, although Harroun's Marmon Wasp was notable for being a single-seater even back then. But we can define several eras of the race by the cars themselves. Engine size was the limiting factor at first, being progressively reduced over the first few years as internal combustion technology was refined and speed built up. With 100 races on the books, discussing all the technical innovations over the years would fill a book, but here are some notable standouts.

Audi made a lot of waves in 2006 when it won Le Mans with its diesel-powered R10, but diesel engines showed up 75 years earlier, to compete in the 1931 Indy 500. The car was another Duesenberg, this time with a 5.8L Cummins diesel engine up front. This was a reaction to new rules for the race—known as the "junkyard formula"—that encouraged more home-grown mechanics and engineers to enter the race. It wasn't spectacularly fast, but it was frugal; Dale Evans and his riding mechanic Thane Hauser were able to do all 200 laps on a single tank of fuel.

The most dominant engine in Indy's history is the four-cylinder Offenhauser. Designed by Fred Offenhauser and Harry Miller, the engine first showed up at the Brickyard in 1933 but had its roots in a pre-WWI Peugeot engine. Miller had built successful inline eight-cylinder engines for Indy racers in the 1920s, winning for the first time (in a Duesenberg) in 1922. After Miller went broke following the crash of 1929, Offenhauser took over development of his engines, eventually creating the double-overhead cam "Offy." Kelly Petillo first took an Offy to victory lane in 1935. Over the years, cars powered with versions of this engine won a total of 27 times—including every year between 1948 and 1964—with its last win coming in 1976.

Those Offy-powered cars that ruled Indy until the 1960s were commonly known as roadsters, and like Harroun's Marmon Wasp, the engine was up front ahead of the driver. But over in Europe there was a revolution going on. In Formula 1, John Cooper decided to move the engine behind the driver, and the advantages it brought were undeniable; before too long, every F1 car was mid-engined. Cooper brought a car to Indianapolis (which between 1950 and 1960 was actually part of the F1 world championship), and thus the seeds were sown on this side of the Atlantic.

Cooper's cars never won the 500, but Colin Chapman's Lotus team—lured by the large winners purse—changed the race forever. Jim Clark drove a mid-engined Lotus to second place in 1963. He probably would have won in 1964 had the car not broken. But he drank the winner's milk the following year, powered to victory by a 4.2L Ford V8. The days of front-engined cars winning the Indy 500 were over.

For a brief moment, it looked like the internal combustion engine might go the same way. In 1967, Parnelli Jones blew the opposition away in the STP-Paxton Turbocar—or at least he did until four laps from the end, when a transmission bearing let go. Designed by Andy Granatelli, the car featured all-wheel drive and a Pratt & Whitney gas turbine engine. The following year, Chapman took up Granatelli's mantle with his Lotus 56. This also had all-wheel drive and a Pratt & Whitney turbine, wrapped in a wedge-shaped body. Although the Lotus 56 didn't win, it resulted in turbine cars being banned from the race.

Few race car builders have pushed the envelope as much as "Smokey" Yunick. In 1959, he took an Offy engine and turned it around, figuring that reversing the torque direction (from counter-clockwise to clockwise, when viewed from the front) would benefit handling on the oval. But his 1964 entrant was far stranger. Known as the capsule car or pod racer, the driver sat in a pod mounted to the left of the chassis. Sadly, the car hit the wall during qualifying and we never got to find out if the idea had legs.

By the early 1970s, Indycars—like their F1 cousins—were cornering faster and faster thanks to slick tires and aerodynamic downforce. Roger Penske's eponymous team was the first to stamp its authority on the slicks-and-wings era starting with Mark Donohue's win in 1972, but it's a much more recent Penske car that really stands out for us. After a careful study of the rules, Penske realized that although everyone was using overhead-cam engines, the traditional American pushrod V8 was still technically eligible. What's more, pushrod V8s were allowed to be bigger (3.4L vs. 2.65L for DOHC V8s) and could also run more boost pressure from their turbochargers. Penske contracted with Mercedes to build just such an engine (the Mercedes 500I) which conservatively made at least 200hp more than the 800hp units built by Ford, Buick, and others. Needless to say, Penske driver Al Unser, Jr won that year's race, the 10th Indy 500 win for the team (which has since gone on to take 1st place another six times).

Today, all 33 cars—and there are just 33—use identical chassis, built by Dallara. Chevrolet and Honda provide the engines and "aero kits"—wings and body panels that visually differentiate the two makes somewhat. The engines are 2.2L turbocharged V6s running on E85 gasoline, good for 550hp (410kW) as a base, although the boost can be increased to 575hp (429kW) up to 10 times during the race via a button on the steering wheel (what we call "push to pass"). They weigh just 1.545lbs (701kg), making them lighter than a current Formula 1, which has more power but also has to carry around a heavy hybrid system.

All 33 cars use the same Firestone racing tires. Firestone (now owned by Bridgestone) is something of an Indy tradition itself, having been involved with the race all the way back to 1911. They're made in Akron, Ohio, and the teams will go through 5,000 tires over the month of May. Each of the four tires on the car is subtly different to one another—the demands made of the front right being different to the front left and so on, and although Firestone's Dale Harrigle wouldn't discuss the specifics of how they compound or construct those tires with Ars, he told us that the lessons it learns on the track do trickle down into the rubber that we use on the street.

Speeds are a little slower than the all-time peak, but not by that much. This year, James Hinchcliffe secured pole position in qualifying (when the cars run with as little downforce—and therefore drag—as possible) for Sam Schmidt's team with a four-lap average of 230.760mph (371.372km/h). It's not bad for a driver who very nearly died in the run up to 2015's race when a part failed, causing the suspension component to pierce the safety cell and impale him.